Etude de l'effet des parametres d'operation sur la microstructure et la resistance au poudrage de revetements galvanises et allies (French text)

Galvanized and galvannealed samples were prepared with the Noranda Technology Center simulator. The heat cycle was similar to the one used in the industry. The substrates used were: ultra low carbon (ULC) and interstitial free (IF-Ti and IF-Ti/Nb). The galvanizing baths were under saturated in iron and contained: 0.10%, 0.12%, 0.14% and 0.16% of aluminum. The galvannealing temperatures were: 460{dollar}spcirc{dollar}C, 490{dollar}spcirc{dollar}C and 530{dollar}spcirc{dollar}C.; The samples were studied by x-ray diffraction and SEM coupled with image analysis. The first campaign showed that the iron content in the bath has an influence at the beginning of the Fe-Zn reaction but, for completely galvannealed sample, there are no significant differences. The second campaign consists of partly galvannealed sample. It was shown that the IF substrates were more reactive than the ULC for all aluminum levels and temperatures. The initial growth of Fe-Zn intermetallics for temperatures under 490{dollar}spcirc{dollar}C is by {dollar}zeta{dollar} phase which transforms into outbursts. These outbursts coalesce and cover the entire surface of the substrate. This growth mechanism has been observed for all the aluminum levels and substrates.; The third campaign was realized to determine the operational conditions (microstructure of the coating) which gives the best powdering resistance (60{dollar}spcirc{dollar} V bend tests). (Abstract shortened by UMI.)...